Multicast meeting unit and multicast meeting program

ABSTRACT

The invention provides a television meeting unit that is capable of displaying a picture smoothly on a middle participation terminal. To realize such television meeting unit, the multicast meeting unit is provided with a picture coding means for coding an input picture, a picture transmission means for transmitting the coded picture by mean of multicast, a picture receiving means for receiving the transmitted coded picture, a picture decoding means for decoding the received picture, a picture display means for displaying the decoded picture, a middle participation notice means for notifying middle participation in a meeting, and a middle participation terminal detection means for detecting the middle participation notice and for transmitting it to the picture coding means. The picture coding means, upon receiving the middle participation notice from the middle participation terminal detection means, changes the coding format to the in-frame coding format.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a television meeting unit, a televisionmeeting system, and a method for controlling a television meetingsystem, and particularly relates to a television meeting unit, atelevision meeting system, and a method for controlling a televisionmeeting system capable of shortening the time required to display apicture of meeting participants to a new participant who participates inthe middle of a meeting.

2. Description of Prior Art

Heretofore, a unit for multiplying the picture and voice at multiplepoints, namely so-called MCU (Multipoint Control Unit), is needed tohold a television meeting between multiple points.

However, with development of the Internet recently, the group broadcastfunction so-called multicast has been available, and as the result itbecomes possible by use of the multicast to hold an electronic meetingbetween multiple points without preparation of a particular unit such asMCU.

FIG. 1 and FIG. 2 show a typical exemplary structure of a multicasttelevision meeting system that uses the picture and voice. FIG. 1 showsa connection diagram to a network, and FIG. 2 is a functional blockdiagram for showing a schematic structure of terminal unit. The pictureand voice generated from the respective terminal units 12-1 to 12-x aretransmitted broadcasterly to the respective terminal units 12-1 to 12 x,and the received picture and voice are displayed individually or in thesynthesized form to realize the television meeting.

The picture and voice of a television meeting system in the form ofcompressed code are transmitted usually because of the communicationcapacity restriction. Typically, H. 261 format or MPEG1 format is usedas the picture compression coding system. In these picture compressioncoding systems, the in-frame coded picture in which the pixel value iscoded as it is and the inter-frame prediction coded picture are usedwith switching selectively. The time redundancy of the picture withslight motion and change is reduced by use of the inter-frame predictioncoded picture in which the difference between the previous frame and thenext frame is coded because the next frame is very similar to theprevious frame. On the other hand, in the case of the picture with quickmotion or scene change, the in-frame coded picture is used effectivelyin which the pixel value is coded as it is used effectively because thecorrelation between frames is slight. In the general television meeting,the in-frame coded picture is transmitted at first and then theinter-frame coded picture is transmitted thereafter because the motionis not so quick.

At first in the case that a participant terminal participates in themiddle in the conventional multicast meeting unit, the new participantreceives the inter-frame prediction coded picture that is the meetingdata served up to that time. Therefore, the terminal that participatesin the middle and receives the inter-frame prediction coded picturecannot display a normal picture because no reference picture (in-framecoded picture) is available, or cannot display the picture until itreceives an in-frame coded picture.

At second in the case that the processing capability of the newparticipant terminal is different, it is required for every participantterminal to perform with a set value within the processable range andfurthermore it is required to change the set value due to the middleparticipation.

SUMMARY OF THE INVENTION

To solve the above-mentioned problem, the present invention is providedwith a function that a middle participation information is transmittedwhen a terminal (middle participation terminal) participates in ameeting in the middle, and other terminals (already participatingterminal) receive and detect the information and transmit the in-framecoded picture (I-frame) instead of the inter-frame prediction codedpicture when the already participating terminals transmit the data.Thereby, it becomes possible to display a picture smoothly (a picture ofa meeting can be displayed in a short time) to the terminal thatparticipates in the middle and the multiple point television meeting isheld smoothly by use of a multicast meeting unit.

Furthermore, the present invention is provided with a function that theprocessing capability information on terminals that are participating ina meeting and terminals that are to participate in the meeting is held,collated, and converted to the coded parameter that is processable byany terminal. Thereby, the information is converted so as to beprocessable by any terminal in the case that it is required to convertthe coding parameter due to the middle participation.

Furthermore, the present invention is provided with a function that thepriority adding function to terminals that precipitate in a meeting andterminals that are to participate in the meeting, and the codingparameter of the important data is converted. Thereby, the individualterminals are coded correspondingly to the priority, and the importantsubject is discussed preferentially in the meeting.

Furthermore, the present invention is provided with a function that thepriority of the terminals are managed so as to avoid the band over dueto I-frame broadcast transmission by adjusting the middle participationand the terminal performance difference to transmit I-frame from theterminal of the higher priority. Thereby, a picture of the terminal ofthe higher priority is displayed first, and the picture of other meetingparticipants is displayed later, and as the result a picture of theterminal of higher priority can be displayed earlier without adverseeffect on the band of the network.

Therefore, the first object of the present invention is to shorten thetime for waiting the display of a picture received by the middleparticipation terminal in a multicast meeting unit.

The second object of the present invention is to make the codingparameter acceptable to every terminal even in the case that the codingparameter, which has been used by every terminal, becomes unacceptableto a part of terminals due to the middle participation in the meeting.

The above-mentioned objects and advantages of the present invention willbe apparent based on the embodiments described in detail hereinafterwith reference to the drawings.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a functional block diagram showing the connection of aconventional multicast multiple point meeting system to a network.

FIG. 2 is a functional block diagram showing the schematic structure ofthe terminal unit of the conventional multicast multiple point meetingsystem.

FIG. 3 is a functional block diagram showing the schematic structure ofa multicast meeting unit in accordance with the first embodiment of thepresent invention.

FIG. 4 is a diagram showing the data structure of a transmitterinformation in the first embodiment.

FIG. 5 is a functional block diagram showing the schematic structure ofa multicast meeting unit to which a reception notice detection means isadded in the first embodiment.

FIG. 6 is a functional block diagram showing the schematic structure ofa multicast meeting unit to which a network error rate measurement meansis added in the first embodiment.

FIG. 7 is a diagram showing a method of middle participation notice byuse of multicast in the first embodiment.

FIG. 8 is a diagram showing a method of middle participation notice byuse of unicast in the first embodiment.

FIG. 9A and FIG. 9B are diagrams showing the picture coding formattransmitted in the present invention, in which FIG. 9A represents thepicture coding format in the case that a multicast meeting is continuingwithout the middle participation, and FIG. 9B represents the picturecoding format that is converted from P-picture coding to I-picturecoding in the case that a middle participation notice is detected duringthe meeting.

FIG. 10 is a functional block diagram showing the schematic structure ofa multicast meeting unit in accordance with the second embodiment of thepresent invention.

FIG. 11 is a diagram showing the data structure of the priorityinformation in the second embodiment.

FIG. 12 is a diagram showing the table structure that holds the picturecoding information, the state that appears when a terminal participatesin a meeting in the middle and when a terminal withdraws from themeeting, and one example of the picture coding format used in themeeting at that time.

FIG. 13 is a functional block diagram showing the schematic structure ofa multicast meeting unit in accordance with the third embodiment of thepresent invention.

FIG. 14 is a functional block diagram showing the schematic structure ofa multicast meeting unit (cellular telephone) in accordance with thefourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to FIG. 3 to FIG. 14. The present invention is by no meanslimited to these embodiments, and can be applied with variousmodifications without departing from the spirit and the scope of thepresent invention.

(First Embodiment)

At first, the configuration for displaying a picture smoothly on aterminal that participates in a meeting in the middle will be describedhereinafter. FIG. 3 is a functional block diagram showing the schematicstructure of the first embodiment of a multicast television terminalunit (simply referred to as “terminal unit” hereinafter depending on thecase) of the present invention. In FIG. 3, 100 denotes a terminal unit,and the terminal unit is connected to a network and used like the systemshown in FIG. 1. The terminal unit 100 supplies a picture data obtainedfrom a picture input means 101 to a picture coding means 102, thepicture coding means 102 compresses and codes the supplied picture dataand supplies it to a picture transmission means 103, and the picturetransmission means 103 transmits the compressed and coded picture datato the network. At that time, the picture coding means 102 changes thecoding method when it obtains a middle participation information from amiddle participation detection means 113.

Similarly, the terminal unit 100 supplies the voice data obtained from avoice input means 104 to a voice coding means 105, the voice codingmeans 105 compresses and codes the supplied voice data and supplies itto a voice transmission means 106, and the voice transmission means 106transmits the compressed and coded voice data to the network. A picturereceiving means 107 receives the compressed and coded picture data fromthe other terminal unit and supplies it to a picture decoding means 108.A plural number of picture decoding means 108 corresponding to thenumber of other terminal units are provided, each picture decoding means108 codes the compressed and coded picture data so as to match with acorresponding terminal and supplies it to a picture display means 109.The number of picture display means 109 corresponds to the number ofother terminal units. Each picture display means 109 displays a pictureof a corresponding terminal.

Similarly, a voice receiving means 110 receives the compressed and codedvoice data from the other terminal unit, and supplies it to a voicedecoding means 111. The number of voice decoding means 111 correspondsto the number of other terminal units. Each voice decoding means 111decodes the compressed and coded voice data for a correspondingterminal, and supplies it to a voice output means 112. The number ofvoice output means 112 corresponds to the number of other terminalunits. Each voice output means 112 outputs the voice of a correspondingterminal. A middle participation notice means 114 supplies a middleparticipation notice to the network when a terminal unit participates inthe middle. FIG. 4 shows an example of a picture data packet to which atransmitter information has been added that is transmitted by the middleparticipation notice means 114. An example of the middle participationnotice data, which is transmitted when a middle participation isnotified, includes the data in which an address information on atransmittee and a transmitter information on a middle participationterminal are placed adjacently.

FIG. 5 is a functional block diagram showing the schematic structure towhich a reception notice detection means is added. In FIG. 5, 116denotes a reception notice transmission means for transmitting areception notice when a middle participation terminal receives anin-frame coded picture from the other meeting terminal, and 115 denotesa reception notice receiving means of a (the other) meeting terminal forreceiving a reception notice that has been transmitted from a middleparticipation terminal through the reception notice transmission means116 (described in detail hereinafter).

FIG. 6 is a functional block diagram showing the schematic structure towhich a network error rate measurement means has been added. In FIG. 6,117 denotes a network error rate measurement means for measuring thenetwork error rate when the picture data is obtained from the picturereceiving means 107 (described in detail hereinafter).

FIG. 7 shows a method of middle participation notice that uses themulticast, and FIG. 8A and FIG. 8B show methods of middle participationnotice that use the unicast. Furthermore, FIG. 9A and FIG. 9B showcoding formats that code a picture signal transmitted from the picturecoding means 102. Out of these figures, FIG. 9A is a diagram for showinga coding format of a transmitted picture signal that is usedconventionally and is used when a multicast meeting is continued withouta middle participation in the present invention. Furthermore, FIG. 9B isa diagram for showing a method for changing the P-picture coding formatto the I-picture coding format when a middle participation notice isreceived during the middle of a meeting, which is employed in thepresent invention. In FIG. 9A and FIG. 9B, I denotes the I-picture(in-frame coded picture), and P denotes the P-picture (inter-frameforward prediction coded picture).

The operation will be described herein under on the terminal unit havingthe above-mentioned structure. The picture data supplied from thepicture input means 101 such as a camera is supplied to the picturecoding means 102. The picture coding means 102 changes the coding formatas described hereinafter based on the information supplied from themiddle participation means 113, and compresses and codes the picturedata. The compressed and coded picture data is transmitted to thenetwork from the picture transmission means 103 by use of the multicast.

The voice data supplied from the voice output means 104 such as amicrophone is supplied to the voice coding means 105. The voice codingmeans 105 compresses and codes the voice data. The compressed and codedvoice data is transmitted to the network from the voice transmissionmeans 106 by use of the multicast. The picture data transmitted from theother terminal unit is received by the picture receiving means 107through the network. The picture receiving means 107 supplies thereceived picture data to the picture decoding means 108-1˜ncorresponding to the respective other terminal units with reference tothe transmitter information on the picture data. One example of thetransmitter information that is embedded in the data to be transmittedis shown in FIG. 4. The number of picture decoding means 108-1˜ncorresponds to the number of other terminal units. Each picture decodingmeans decodes the picture data to be transmitted to the picture displaymeans 109-1˜n. The number of picture display means 109-1˜n correspondsto the number of other terminal units. Each picture display meansdisplays the decoded picture data on a display.

The voice data transmitted from the other terminal unit is received bythe voice receiving means 110 through the network. The voice receivingmeans 110 supplies the received voice data to the voice decoding means111-1˜n corresponding to the respective other terminal units withreference to the transmitter information on the voice data in the samemanner as used in the case of the picture data. The number of voicedecoding means 111-1˜n corresponds to the number of other terminalunits. Each voice decoding means decodes the voice data and supplies itto the voice output means 112-1˜n. The number of voice output means112-1˜n corresponds to the number of other terminal units. Each voiceoutput means outputs the decoded voice data from a speaker. Otherwise, amethod, in which one terminal is provided with not a plurality of voiceoutput means, but one terminal is provided with one voice output meansby providing a voice synthesis means so-called mixer between the voicedecoding means and the voice output means, may be employed.

When the terminal unit participates in a meeting in the middle, themiddle participation notice means 114 notifies the other terminals ofthe middle participation through the multicast or unicast.

In the case that the middle participation is notified through themulticast, the middle participation notice means 114 notifies the otherterminals of the middle participation simultaneously as shown in FIG. 7.On the other hand, in the case that the middle participation is notifiedthrough the unicast, two methods may be available as shown in FIG. 8. Inthe one method, the address of meeting terminals that are participatingin a current meeting has been obtained previously and the middleparticipation is supplied individually as shown in FIG. 8A. In the othermethod, the middle participation is supplied to any one meeting terminalamong meeting terminals that are currently participating in a meetingand the meeting terminal that has received the middle participationpropagates it to the other meeting terminal successively as shown inFIG. 8B.

<Method for Changing Coding>

Methods shown in FIG. 9A and FIG. 9B are exemplified as the method forchanging the coding format in the picture coding means 102.

In the case of the conventional transferred picture coding format asshown in FIG. 9A, a middle participation terminal receives a P-picturebecause terminals that are participating in a meeting currently transmitthe P-picture when the middle participation terminal participates in themeeting in the middle. The middle participation terminal that receivesthe P-picture cannot decode a normal picture because the middleparticipation terminal has no I-picture, which is the reference picture.

However, it is possible to change the coding method when a middleparticipation terminal participates in a meeting in the middle becausecurrent participation terminals receive a middle participation notice.Therefore, the current terminals that are participating in the meetingreceives the middle participation notice at the middle participationdetection means 113 when the middle participation terminal participatesin the meeting in the middle, and the information is supplied to thepicture coding means 102. In response to the information, the picturecoding means 102 that has continued coding to P-picture until nowchanges the coding format to I-picture that can be decoded singularly.

<Method for Setting I-Picture Sending Term>

Three I-picture sending terms are available as described herein under.

In the first method, the I-picture is sent for a certain time. One framepicture data of changed coding method or a certain number of frames ofchanged coding method is sent out, and the coding method is changed tothe original coding method thereafter. In the second method, when themiddle participation terminal receives an in-frame coded picture fromother meeting terminals, the middle participation terminal issues areception notice to other meeting terminals, and other meeting terminalschange the coding method to the original coding method. The secondmethod will be described with reference to FIG. 5.

When the picture receiving means 107 of the middle participationterminal receives an I-picture from other meeting terminals, theinformation for notifying the reception is supplied to the receptionnotice transmission means 116. The reception notice transmission means116 transmits a reception notice to other meeting terminals by use ofthe multicast as shown in FIG. 7 or by use of the unicast as shown inFIG. 8A. When the unicast is used, the transmitter information shown inFIG. 4 included in the received I-picture is used to specify thetransmitter.

Other meeting terminals receive the reception notice through thereception notice receiving means 115, the information for notifyingreception of the reception notice is supplied to the picture codingmeans 102, and the picture coding means 102 changes the picture codingformat to the original format.

Because other meeting terminals can recognize that the middleparticipation terminal has received the reference picture (I-picture),other meeting terminals can continue to transmit the reference pictureuntil the middle participation terminal receives the reference picture.

In the third method, the network error rate is measured, other meetingterminals continue to use the changed coding format and transmit thereference picture for only the time corresponding to the error rate. Thethird method will be described with reference to FIG. 6.

The network error rate measurement means 117 measures the error rate inthe picture data received through the picture receiving means 107 basedon, for example, the sequence number embedded in the picture data, andthe measured error rate is supplied to the picture coding means 102. Thepicture coding means 102 determines the reference frame sending termshown in FIG. 9 depending on the error rate supplied from the networkerror rate measurement means 117. In detail, the doubled reference framesending term may be employed for the doubled error rate. For example, ifthe reference picture of two frames is transmitted at the time of themiddle participation under the condition that one packet error isincluded in 100 packets, the reference picture of doubled, namely four,frames is transmitted at the time of the middle participation when theerror rate is doubled (the condition that two packet errors are includedin 100 packets).

Because the picture receiving means 107 receives the picture data from aplurality of meeting terminals, the mounting method that satisfy thehighest error rate may be employed. It is apparent that this method maybe used for the middle participation terminal and other meetingterminals. Thereby, a plurality of I-picture, namely reference picture,can be sent out in the case that the network error rate is high, theprobability of reception of the reference picture by the middleparticipation terminal is improved with minimized load on the network.By using the structure described hereinbefore, it is possible to displaythe picture of a meeting within a short time by use of the multicasttelevision meeting unit even though a terminal participates in themeeting in the middle, and the multiple point television meeting can becontinued smoothly.

(Embodiment 2)

Next, a mechanism for exchanging the processing capability informationon each terminal so that all the terminals participating in a meetingcan display the picture and a mechanism for giving the priority to thedata that is important in the meeting will be described. FIG. 10 is afunctional block diagram showing the schematic structure of the secondembodiment of a multicast television meeting terminal unit of thepresent invention. In FIG. 10, 800 denotes a terminal unit, and theterminal unit is connected to a network and used.

The terminal unit 800 supplies the picture data obtained from a pictureinput means 801 to a picture coding means 802, the picture coding means802 compresses and codes the supplied picture data and supplies it to apicture transmission means 803, and the picture transmission means 803transmits the compressed and coded picture data to the network. At thattime, the picture coding means 802 obtains a middle participationinformation from a picture receiving means 807 and changes the codingmethod. The terminal name of the middle participation terminal and thepicture data (coding format, parameter) transmitted from the middleparticipation terminal are held in a coding state holding means 813.

Similarly, the voice data obtained from a voice input means 804 issupplied to a voice coding means 805, the voice coding means 805compresses and codes the supplied voice data and supplies to a voicetransmission means 806, and the voice transmission means 806 transmitsthe compressed and coded voice data to the network. At that time, theinformation such as voice level is supplied from the voice input means804 to an significance information adding means 814. Furthermore, thevoice coding means 805 obtains the voice coding format or voice codingparameter from a voice receiving means 810 and changes the codingmethod. Furthermore, the picture receiving means 807 receives thecompressed and coded picture data from the other terminal unit throughthe network, and supplies it to a picture decoding means 808. At thattime, the received picture information is supplied to the picture codingmeans 802. The number of picture decoding means 808 corresponds to thenumber of other terminal units, and the compressed and coded picturedata is decoded so as to match with each terminal and supplied topicture display means 809. The number of picture display means 809corresponds to the number of other terminal units. The picture displaymeans displays a picture of each terminal.

Similarly, the voice receiving means 810 receives the compressed andcoded voice data from the other terminal unit through the network, andsupplies it to a voice decoding means 811. The number of voice decodingmeans 811 corresponds to the number of other terminal units, and thecompressed and coded voice data is decoded so as to match with eachterminal and supplied to a voice output means 812. The number of voiceoutput means 812 corresponds to the number of other terminal units. Thevoice output means outputs the voice of on each terminal.

<Significance Information Addition>

FIG. 11 shows one example of a picture data packet that is to betransmitted to which the significance information is added. FIG. 12shows an example of the structure of a table for holding the picturecoding information, the state of middle participation and middlewithdrawing, and the picture coding format used in the meeting at thattime.

The operation of the terminal unit having the structure describedhereinabove will be described herein under.

The picture data taken in from the picture input means 801 such ascamera is supplied to the picture coding means 802, and the picture datais compressed and coded.

A method described hereinunder, in which the middle participation isdetected by the picture receiving means 807 without using the middleparticipation notice means 114 as in the case of the embodiment 1 whenthe picture coding means 802 compresses and codes the picture data, maybe employed.

The picture receiving means 807 refers the transmitter information onthe received picture data as shown in FIG. 4. If the transmitterinformation is a transmitter information on a terminal other thancurrent participation terminals, the transmitter information is judgedas that of a middle participation terminal, and the information fornotifying participation of the middle participation terminal is suppliedto the picture coding means 802.

As an exemplary “method for discrimination between the currentparticipation terminal and the middle participation terminal”, a methodin which the transmitter information on the current participationterminals is stored in a memory of each terminal may be employed. In thecase that the data having the transmitter information that is not storedin the memory is supplied, it is possible to judge the data to indicateparticipation of a middle participation terminal.

The middle participation is detected as described hereinabove, and thepicture coding means 802 changes the coding format to the in-frame codedpicture (reference picture) as shown in FIG. 9. As the result, it ispossible to display the picture of other meeting terminals on the middleparticipation terminal within a short time.

The compressed and coded picture data is transmitted to the networkthrough the picture transmission means 803. The picture transmissionmeans 803 can add the significance to the picture data as shown in FIG.11 when the picture data is transmitted. The significance represents thedynamic significance in the meeting such as a speaker. A method may beemployed, in which when the level of significance of a speaker is up,the voice input level supplied from the voice input means 804 issupplied to the significance information adding means 814, and thesignificance information adding means 814 adds the significancecorresponding to the voice level. The picture quality is improved, theframe rate is increased, or the picture size may be changed by use ofthe picture coding means 802 for the case of the picture data of highsignificance.

For example, the processing is performed normally at a performance value(parameter): B that is lower than the performance value (parameter): Aof the terminal having the lowest performance based on the processingcapability information exchange (<that will be described hereinafter as<parameter setting relevant to the processing capability of theterminal>) with emphasis on the saving of NW band and immediate dataprocessing, and only when the data to which the significance is addedcomes, the level of the performance value is up to a higher value withina range lower than the performance value A for the data withsignificance. As described hereinabove, the quality of the picturesupplied from a terminal that is considered to be important such as aspeaker in the meeting is changed dynamically, and as the result thequality of a picture that attracts attentions of participants isimproved. The voice data supplied from the voice input means 804 such asa microphone is supplied to the voice coding means 805. The voice codingmeans 805 compresses and codes the voice data. The compressed and codedvoice data is transmitted to the network by use of the multicast throughthe voice transmission means 806.

The picture data transmitted from other terminal units is received bythe picture receiving means 807 through the network. The picturereceiving means 807 supplies the received picture data to the picturedecoding means 808-1˜n corresponding to the respective other terminalunit with reference to the transmitter information on the picture data.The number of picture decoding means 808-1˜n corresponds to the numberof other terminal units. Each of the picture decoding means 808-1˜ndecodes the picture data and supplies it to the picture display means809-1˜n. The number of picture display means corresponds to the numberof other terminal units similarly, and the decoded picture data isdisplayed on a display.

The voice data transmitted from the other terminal units is received bythe voice receiving means 810 through the network. The voice receivingmeans 810 supplies the received voice data to the voice decoding means811-1˜n corresponding to the respective terminal units with reference tothe transmitter information on the voice data. The number of voicedecoding means 811-1˜n corresponds to the number of other terminalunits. Each of the voice decoding means 811-1˜n decodes the voice dataand supplies it to the voice output means 812-1˜n. The number of voiceoutput means 812-1˜n corresponds to the number of other terminal unitssimilarly, and the decoded voice data is outputted from a speaker. Insome cases a method may be employed, in which one terminal is providedwith not a plurality of voice output means, but one terminal is providedwith only one voice output means with aid of a voice synthesis meansso-called mixer interposed between the voice decoding means and thevoice output means.

Examples of the significance addition includes a case in whichsignificance is added depending on the user, that is, the significanceis up for the user of the chairman, and a case in which a highsignificance is added to a terminal displaying the significant picturemotion, other than the case in which the high significance is addeddepending on the input level of the voice. Furthermore, a method inwhich the picture coding means 802 changes the picture coding formatwill be described herein under. A method shown in FIG. 9 is exemplifiedas a method in which the picture coding means 802 changes the codingformat similarly to the embodiment 1.

<Parameter Setting Relevant to Processing Capability of ParticipationTerminal>

The processing capability information exchange will be described as thepremise for adding the above-mentioned significance. A middleparticipation terminal codes the data by use of the coding format andparameter that are relevant to the processing capability (CPUperformance) and supplies it to other meeting terminals. The othermeeting terminals that have received it obtain the picture size, thenumber of frames, and the data quantity of the received pictureinformation, and then changes the coding format so as to fit thereceived data, and as the result the other meeting terminals can supplythe data that is relevant to the processing capability of the middleparticipation terminal.

A method for changing the coding will be described in detail withreference to FIG. 12A, FIG. 12B, and FIG. 12C. At first, in the initialstate of a meeting shown in FIG. 12A, terminals A, B, and C areparticipant in the meeting. In this state, because the picture codingparameter sent from the terminal A is lowest, the picture coding formatCIF, 10 fps, and 64 bps, that is the picture coding format of theterminal A, is used as the picture coding format in the meeting. Herein,the picture size CIF represents 352 (pixels)×288 (pixels), and QCIFrepresents 176 (pixels)×144 (pixels).

Next, the state in which the terminal D (QCIF, 5 fps, 32 kbps)participates in the meeting in the middle is shown in FIG. 12B. Herein,because the processing capability of the terminal D is lowest, thepicture coding format of the terminal D that is lowest in the processingcapability is used in the meeting in the same manner as used previously.Next, the state in which the terminal A and the terminal D withdraw fromthe meeting in the middle is shown in FIG. 12C. The data of the terminalA and the terminal D that have withdrawn from the meeting is deletedfrom the table, the picture coding information on the terminal C havingthe lowest processing capability among the residual terminals is usedsimilarly, and the meeting is continued by the residual meetingterminals. The level of the processing capability is defined in terminalunits herein. The reason is that all the values of the respective codinginformation are lower than those of other terminals. In the case thatthe terminal T1 has the picture size of the lowest value t1, theterminal T2 has the frame rate of the lowest value t2, and the terminalT3 has the bit rate of the lowest value t3, (t1, t2, and t3) are used asthe parameter for decision.

H. 323 capacity exchange has been known as a conventional method fordetermining parameters used by each terminal as described hereinabove.In this method, after each terminal extends the session, parameters thatcan be encoded and decoded are exchanged each other and a meeting iscontinued by use of parameters that are usable each other. This methodis possible only for 1:1 meeting, and IMCU should be used for using thismethod in the case that three or more terminals participate. In thiscase, at first, each terminal transmits parameters that can be encodedand decoded to MCU. Next, MCU detects parameters that can be acceptablefor all the terminals based on the parameters supplied from eachterminal, and transmits the parameter to each terminal. Each terminalparticipates in the meeting by use of the parameters that have beendetected by MCU.

However, because the structure of the present embodiment does not useMCU, this method is not applied. In the present embodiment, themulticast address is acquired from DHCP server, and the picture andvoice are transmitted immediately. The parameter is changed to theparameter that is usable each other on the terminal side that hasreceived the picture and voice. Because each terminal decides theparameter based on the supplied picture and voice as describedhereinabove, the structure having no MCU can be employed. Furthermore,in the conventional method, all the terminals should transmit parametersto MCU, MCU re-detects the parameter that is usable for all theterminals and distributes the parameter to each terminal in the case aterminal participates in the meeting in the middle. However, in the caseof the present embodiment, these procedures can be eliminated, a middleparticipation terminal can transmit the picture and voice immediately,and the time required for the middle participation terminal toparticipate in the meeting is shortened.

The same is applied to the voice data, the middle participation terminalcodes the voice data by use of the coding format and parameter that arerelevant to the processing capability and supplies it to other meetingterminals, the other meeting terminals that receive it obtain the codingformat and coding parameter of the received voice information and changethe coding to the relevant coding to thereby supply the data that isrelevant to the processing capability of the middle participationterminal. As described hereinabove, in the present embodiment, bychanging the coding method to a method that is relevant to the receivedcoding format (change the coding parameter), it is possible to continuea meeting (the meeting data is displayed even on a terminal having thelow processing capability) when a meeting terminal having a lowprocessing capability participates in the meeting in the middle.Furthermore, by using the significant information, the high significantpicture such as the picture of a speaker is displayed with higherpicture quality.

The middle participation detection means 113 described in the,embodiment 1 and the coding state holding means 813 described in thesecond embodiment 2 may be used in combination to receive the middleparticipation notice through the middle participation detection means113. In this case, an exemplary method, in which the current codinginformation is held in the coding state holding means 813 and the codingformat is changed, may be realized.

(Embodiment 3)

Next, a mechanism for avoiding the inconvenience that the band isoccupied fully when all the terminals that are participating in ameeting transmit I-frame simultaneously in response to reception of anotice of middle participation will be described herein under.

FIG. 13 is a functional block diagram showing the schematic structure ofthe third embodiment of a multicast television meeting terminal unit ofthe present invention.

In FIG. 13, 1100 denotes a terminal unit, and the terminal unit isconnected to the network and used as in the case of the system shown inFIG. 1. The terminal unit 1100 supplies the picture data obtained from apicture input means 1101 to a picture coding means 1102, the picturecoding means 1102 compresses and codes the supplied picture data andsupplies it to a picture transmission means 1103, and the picturetransmission means 1103 transmits the compressed and coded picture datato the network. At that time, the picture coding means 1102 changes thecoding method depending on the priority supplied from the prioritydecision means 1114. The coding information that is used before thechange is held in the coding state holding means 1113 in the same tableform as used in the embodiment 2.

The voice data obtained from a voice input means 1104 is supplied to avoice coding means 1105, the voice coding means 1105 compresses andcoded the supplied voice data and supplies it to a voice transmissionmeans 1106, and the voice transmission means 116 transmits thecompressed and coded voice data to the network. Furthermore, a picturereceiving means 1107 receives the compressed and coded picture data fromthe other terminal unit through the network, and transmits it to apicture decoding means 1108. At that time, the received pictureinformation is supplied also to the priority decision means 1114. Thenumber of picture decoding means 1108 corresponds to the number of otherterminal units, and the compressed and coded picture data is decoded soas to match with each terminal and supplied to the display means 1109.The number of picture display means 1109 corresponds to the number ofother terminal units similarly, and the picture of each terminal isdisplayed.

Similarly, a voice receiving means 1110 receives the compressed andcoded voice data from the other terminal unit through the network, andsupplies it to the voice decoding means 1111. The number of voicedecoding means 1111 corresponds to the number of other terminal units,and the compressed and coded voice data is decoded so as to match witheach terminal and is supplied to the voice out means 1112. The number ofvoice output means 1112 corresponds to the number of other terminalunits, and the voice of each terminal is outputted.

The operation of the terminal unit having the structure as describedhereinabove will be described hereinafter. The picture data suppliedfrom the picture input means such as a camera is supplied to the picturecoding means 1102. The picture coding means 1102 changes the codingformat based on the priority information supplied from the prioritydecision means 1114, and compresses and codes the picture data.

The priority information is prepared by the priority decision means 1114that has obtained the picture data information from the picturereceiving means 1107. For example, a promoter of the meeting assigns thepriority to each terminal previously at the time before the meeting isheld. In many cases, the terminal of the chairman is assigned a highpriority, and a terminal used by a general participant is assigned a lowpriority. The picture coding means 1102 changes the picture codingformat according to the priority when a middle participation terminal isdetected. For example, when a middle participation terminal is detected,other terminals change the coding format from the in-frame predictioncoded picture to the inter-frame coded picture as shown in FIG. 9. Atthat time, if all the terminal changes the coding format simultaneously,the picture data quantity transmitted through the network increasessharply to result in pressed band. To avoid the above-mentioned problem,the picture is changed to the in-frame coding picture in the ordersuccessively from the terminal having the highest priority fortransmission with reference to the priority information. Thereby, themiddle participation terminal can display the picture in the orderaccording to the priority.

The compressed and coded picture data is transmitted from the picturetransmission means 1103 to the network by use of the multicast. Thevoice data supplied from the voice output means 1104 such as amicrophone is supplied to the voice coding means 1105. The voice codingmeans 1105 compresses and codes the voice data. The compressed and codedvoice data is transmitted from the voice transmission means 1106 to thenetwork by use of the multicast.

The picture data transmitted from the other terminal unit is received bythe picture receiving means 1107 through the network. The picturereceiving means 1107 supplies the received picture data to the picturedecoding means 1108-1˜n corresponding to the respective other terminalunits with reference to the transmitter information on the picture data.The number of picture decoding means 1108-1˜n corresponds to the numberof other terminal units. Each of the picture decoding means 1108-1˜ndecodes the picture data and transmits the picture to the picturedisplay means 1109-1˜n. The number of picture display means 1109-1˜ncorresponds to the number of other terminal units similarly, and thedecoded picture data is displayed on a display.

The voice data transmitted from the other terminal unit is received bythe voice receiving means 1110 through the network. The voice receivingmeans 1110 supplies the received voice data to the voice decoding means1111-1˜n corresponding to the respective other terminal units withreference to the transmitter information on the voice data. The numberof voice decoding means 1111-1˜n corresponds to the number of otherterminal units, and the voice decoding means 1111-1˜n decode the voicedata and supply it to the voice output means 1112-1˜n. The number ofvoice output means 1112-1˜n corresponds to the number of other terminalunits similarly, and the decoded voice data is outputted from a speaker.In some cases a method may be employed, in which one terminal isprovided with not a plurality of voice output means, but one terminal isprovided with only one voice output means with aid of a voice synthesismeans so-called mixer interposed between the voice decoding means andthe voice output means.

For example, a method shown in FIG. 9 that is similar to the methoddescribed in example 1 may be exemplified as a method that is used bythe picture coding means 1102 to change the coding format. In thepresent example, the (a part of) priority information is transmittedfrom the picture receiving means 1107 to the priority decision means1114, but the transmission is not necessarily required. For example, (1)the data transmission from 1107 to 1114 can be eliminated by holding thepriority information previously in the priority decision means 114 (adashed line in FIG. 13 indicates the case). Furthermore, for example,(2) only the information that indicates whether the I-frame is receivedor not (whether a middle participation terminal participates or doesnot) is supplied from the picture receiving means 1107 to the picturecoding means 1102, and the coding method is changed immediately or laterdepending on the information supplied from the priority decision means1114. As described hereinabove, various modifications may be employed.

As described hereinabove, in the present embodiment, by use of thestructure described hereinabove, not only it is possible to display thepicture data of a meeting within a short time as described in theexample 1 but also it is possible that the picture data of the terminalhaving the higher priority can be displayed earlier without pressing ofthe band of the network by use of the priority information. In thelatter case, for example, the picture data with high priority of, forexample, the chairman is displayed earlier and the picture data of othermeeting participants are displayed later generally.

(Embodiment 4)

In the present embodiment, the unit other than personal computers suchas desktop or potable computers can be used as the terminal unit thatcan participates in a meeting (including middle participation). FIG. 14is a functional block diagram showing the schematic structure of thefourth embodiment of a terminal unit of the present invention. Thecellular phone is used as the terminal unit in the present embodiment.In FIG. 14, 400 denotes a cellular phone served as the terminal unit,and the cellular phone 400 is connected to the network and used as inthe case of the terminal unit 100 shown in FIG. 1. The cellular phone400 is provided with a picture input means 101 for receiving a picturesignal, a picture coding means 102 for receiving the picture signal fromthe picture input means 101 and for compressing and coding the picturesignal, a picture transmission means 103 for generating the compressedand coded transmission picture data, and a communication means 250 fortransmitting the compressed and coded picture data generated from thepicture transmission means 103 to the network as in the case of theterminal unit 100 described in the first embodiment.

Furthermore, the cellular phone 400 is provided with a voice input means104 for receiving a voice signal, a voice coding means 105 for receivingthe voice signal from the voice input means 104 and for compressing andcoding the voice signal, and a voice transmission means 106 fortransmitting the compressed and coded voice data to the communicationmeans 250.

Furthermore, the cellular phone 400 is provided with a picture receivingmeans 107 for receiving the compressed and coded picture data suppliedfrom the other cellular phone or terminal unit through the network,picture decoding means 108 for decoding the received picture data, andpicture display means 109 for displaying the decoded picture. The numberof picture decoding means 108 corresponds to the number of othercellular phones, and the supplied picture data is decoded so as to matchwith each cellular phone or terminal unit and is supplied to the picturedisplay means 109. The number of picture display means 109 correspondsto the number of other cellular phones similarly, and the picturedisplay means display the picture on the respective terminals.

Furthermore, the cellular phone 400 is provided with a voice receivingmeans 110, voice decoding means 111, and voice output means 112 forreceiving and reproducing the voice transmitted from the other cellularphone or terminal unit. The voice receiving means 110 receives thecompressed and coded voice data from the other cellular phone orterminal unit through the network and supplies it to the voice decodingmeans 111. The number of voice decoding means 111 corresponds to thenumber of other cellular phones, and the compressed and coded voice datais decoded so as to match with each terminal and supplied to the voiceoutput means 112. The number of voice output means 112 corresponds tothe number of other cellular phones and terminal units similarly. Thevoice output means outputs the voice of each terminals.

Furthermore, the cellular phone 400 is provided with a middleparticipation notice means 114 that is operated when this cellular phoneparticipates in a meeting in the middle, and a middle participationdetection means 113 for detecting a middle participation notice signaltransmitted when the other cellular phone participates in the meeting inthe middle as in the case of the terminal unit in accordance with thefirst embodiment.

The communication 250 has not only a function to control thecommunication between the cellular phone 400 and a base station but alsoa function to transmit the compressed and coded picture data andcompressed and coded voice data to the network and a function to receivethe compressed and coded picture data and compressed and coded voicedata from the network, namely the two-way function. Furthermore, thecommunication means 250 functions to transmit a middle participationnotice signal to the network and to receive a middle participationnotice signal from the network.

Because the cellular phone 400 is provided with the above-mentionedfunction, it is possible for the cellular phone 400 in accordance withthe present embodiment to participate in a multicast meeting. The middleparticipation notice means 114 supplies the middle participationinformation to the communication means 250 through the network when thecellular phone 400 participates in the meeting in the middle. On theother hand, the middle participation detection means 113 receives anddetects a middle participation notice signal transmitted from the othercellular phone from the network through the communication means 250.

The notice and detection of middle participation in a multicast meetingare operated in the same manner as that operated in the firstembodiment. The present invention is applied for potable terminal unitsas the mobile apparatus such as the cellular phone similarly.

In each embodiment, the in-frame coded “picture” detection units areused as the information for detecting middle participation, butotherwise a method in which the rate of the in-frame coded “macro-block”in the picture is detected as the unit to detect middle participationmay be employed. In detail, in the case that the coding format such asMPEG-4 that uses the in-frame coded macro-block is used, not thein-frame coded picture is detected, but the rate of the in-frame codedmacro-block in the picture is detected to detect middle participation.For example, the following detection method is exemplified as a methodfor detecting the in-frame coded macro-block.

At first, the macro-block coding format in the picture is counted.Because the coding format information is stored in each macro-block, themacro-block coding format can be counted easily by referring the codingformat information. Next, the rate of the in-frame coded macro-block inthe picture is counted, and if the rate is equal to a half or more, thenit is judged to be the middle participation.

Furthermore, in each embodiment, the case in which the number of thepicture decoding means, picture display means, voice decoding means, andvoice output means corresponding respectively to the number of otherterminals (hardware or software having such function) are provided isdescribed, but otherwise one hardware or software having such functionperforms these processing by means of time sharing technique in somecases. Therefore, the number of these means is by no means limited.

Furthermore, in each embodiment, (1) coding method represents the typeof codec (CODEC: COmpression/DECompression) such as H. 261, H 263, orMPEG, (2) coding format represents the difference between the in-framecoding (I-frame) and the inter-frame coding (P-frame), and (3) codinginformation (coding parameter) represents the picture size, frame rate,and bit rate. Furthermore, in (3), the coding information is synonymicalfor the coding parameter, but in some cases the coding information isused to represent the item of attribute and the coding parameter is usedto represent the item of attribute value differently (difference betweenthe attribute and attribute value).

The present invention is described based on the preferred embodimentsshown in the drawings, but it will be obvious to those skilled in theart that the present invention can be easily modified and changed invarious ways without departing from the spirit and the scope of theinvention. The present invention includes such various modifications.

What is claimed is:
 1. A multicast meeting unit comprising: a pictureinput means for receiving a picture stream such as a camera; a picturecoding means for coding the input picture stream to prepare the codedpicture information to be transmitted; a picture transmission means fortransmitting the coded picture information to a network by use of themulticast; a picture receiving means for receiving the pictureinformation transmitted by use of the multicast; a picture decodingmeans for decoding the received data; a picture display means fordisplaying the decoded picture stream; a middle participation noticemeans for notifying the middle participation in a meeting; and a middleparticipation terminal detection means for detecting the terminal thatparticipates in the meeting in the middle, and for supplying theinformation to said picture coding means, wherein said picture codingmeans receives the detection signal from said middle participationterminal detection means, and changes the coding format to the in-framecoding format.
 2. A multicast meeting unit comprising: a picture inputmeans for receiving a picture stream such as a camera; a picture codingmeans for coding the input picture stream to prepare the coded pictureinformation to be transmitted; a picture transmission means fortransmitting the coded picture information to a network by use of themulticast; a picture receiving means for receiving the pictureinformation transmitted by use of the multicast; a picture decodingmeans for decoding the received data; a picture display means fordisplaying the decoded picture stream; and a participation terminalstoring means for storing the transmitter information on terminals thatare participating in a meeting, wherein said picture receiving means,upon receiving an in-frame coded picture, notifies said picture codingmeans of the reception, and said picture coding means, upon receivingthe notice from said picture receiving means, changes the coding formatto the in-frame coding format.
 3. The multicast meeting unit accordingto claim 2, wherein said picture receiving means, in the case that areceived in-frame coded picture is found to be an in-frame coded picturetransmitted from a terminal other than terminals stored in saidparticipation terminal information storing means by recognizing theterminal with reference to said participation terminal informationstoring means, notifies said picture coding means of the reception. 4.The multicast meeting unit according to claim 2, wherein said picturecoding means, in the case that a notice supplied from said picturereceiving means is found to be an in-frame coded picture received from aterminal other than terminals stored in said participation terminalinformation storing means as the result of reference to saidparticipation terminal information storing means, changes the codingformat.
 5. A multicast meeting unit comprising: a picture input meansfor receiving a picture stream such as a camera; a picture coding meansfor coding the input picture stream to prepare the coded pictureinformation to be transmitted; a picture transmission means fortransmitting the coded picture information to a network by use of themulticast; a picture receiving means for receiving the pictureinformation transmitted by use of the multicast; a picture decodingmeans for decoding the received data; a picture display means fordisplaying the decoded picture stream; and a coding information storingmeans for storing the coding parameter of terminals that areparticipating in a meeting and terminals that participate in the meetingin the middle if a terminal participates in the meeting in the middle,wherein said picture coding means codes the picture data by use of achanged coding parameter that can be displayed on all the terminals thatare participating in the meeting with reference to said codinginformation storing means.
 6. The multicast meeting unit according toclaim 1, further comprising a priority decision means for deciding andholding the information on the priority of the meeting terminal and forsupplying the information to said picture coding means, wherein saidpicture coding means receives the information from said prioritydecision means and changes the coding format.
 7. The multicast meetingunit according to claim 5, further comprising a significance informationadding means for deciding and holding the information on thesignificance of the information to be transmitted in the meeting and forsupplying the information to said picture coding means, wherein saidpicture coding means receives the information from said significanceinformation adding means and changes the coding parameter.
 8. Themulticast meeting unit according to claim 1, wherein said middleparticipation notice means transmits the middle participationinformation to all the terminals that are participating currently in themeeting by use of the multicast when a terminal participates in themeeting in the middle.
 9. The multicast meeting unit according to claim1, wherein said middle participation notice means transmits the middleparticipation information to all or a part of the terminals that areparticipating currently in the meeting by use of the unicast when aterminal participates in the meeting in the middle.
 10. The multicastmeeting unit according to claim 1, wherein said middle participationterminal detection means detects an in-frame coded picture transmittedfrom a middle participation terminal.
 11. The multicast meeting unitaccording to claim 1, wherein said middle participation terminaldetection means detects the rate of an in-frame coded macro-blocksupplied from a middle participation terminal.
 12. The multicast meetingunit according to claim 1, further comprising a network error ratemeasurement means for measuring the error rate of the network and forsupplying the information on the error rate of the network to saidpicture coding means, wherein said picture coding means changes thecoding format during the time corresponding to the error rate of thenetwork.
 13. The multicast meeting unit according to claim 2, furthercomprising: a reception notice transmission means for receiving a noticeof the in-frame coded picture reception from said picture receptionmeans and for transmitting a reception notice of the in-frame codedpicture; and a reception notice receiving means for receiving areception notice from said reception notice transmission means and forsupplying the reception notice information to said picture coding means,wherein said picture coding means continues the change of the codingformat until said picture coding means receives said reception noticeinformation.
 14. The multicast meeting unit according to claim 1,wherein said picture coding means changes the changed coding format tothe original coding format after a certain time period elapses.
 15. Themulticast meeting unit according to claim 1, wherein said picture codingmeans codes the picture data by use of coding method corresponding tothe coding method of the received picture.
 16. The multicast meetingunit according to claim 1, wherein said picture coding means codes thepicture data with changing the size to the same size as the size of thereceived picture.
 17. The multicast meeting unit according to claim 1,wherein said picture coding means codes the picture data with changingthe number of frames corresponding to the number of frames of thereceived picture.
 18. The multicast meeting unit according to claim 1,wherein said picture coding means codes the picture data with changingthe data quantity corresponding to the data quantity of the receivedpicture.
 19. The multicast meeting unit according to claim 1, furthercomprising: a voice coding means for coding the voice data and forpreparing the coded voice information to be transmitted; a voicetransmission and receiving means for transmitting and receiving thecoded voice information; a voice decoding means for decoding thereceived voice information; and a voice output means for outputting thedecoded voice data, wherein said voice coding means codes the voice datawith changing the coding method corresponding to the coding method ofthe received voice.
 20. The multicast meeting unit according to claim 1,further comprising: a voice coding means for coding the voice data andfor preparing the coded voice information to be transmitted; a voicetransmission and receiving means for transmitting and receiving thecoded voice information; a voice decoding means for decoding thereceived voice information; and a voice output means for outputting thedecoded voice data, said voice coding means codes the voice data withchanging the coding parameter corresponding to the coding parameter ofthe received voice.
 21. A multicast meeting program for carrying outmulticast meeting by a computer to execute the steps of: inputting apicture stream to a picture input means such as a camera of a multicastmeeting unit; coding the input picture stream by a picture coding meansof the multicast meeting unit to prepare the coded picture informationto be transmitted; transmitting the coded picture information by apicture transmission means to a network by use of the multicast; makinga picture receiving means receive the picture information transmitted byuse of the multicast; decoding the received data by a picture decodingmeans of the multicast meeting unit; displaying the decoded picturestream on a picture display means of the multicast meeting unit;notifying that a terminal participates in a meeting in the middle by amiddle participation notice means, if the terminal participates in themeeting in the middle; and detecting the terminal that participates inthe meeting in the middle by a middle participation terminal detectionmeans of the multicast meeting unit, upon receiving the middleparticipation notice, wherein said picture coding means receives thedetection signal from said middle participation terminal detectionmeans, and changes the coding format to the in-frame coding format. 22.A multicast meeting program for carrying out multicast meeting by acomputer to execute the steps of: inputting a picture stream to apicture input means such as a camera of a multicast meeting unit; codingthe input picture stream by a picture coding means of the multicastmeeting unit to prepare the coded picture information to be transmitted;transmitting the coded picture information by a picture transmissionmeans to a network by use of the multicast; making a picture receivingmeans receive the picture information transmitted by use of themulticast; decoding the received data by a picture decoding means of themulticast meeting unit; displaying the decoded picture stream on apicture display means of the multicast meeting unit; and storing thetransmitter information on terminals that are participating in a meetingin a participation terminal storing means, wherein said picturereceiving means, upon receiving an in-frame coded picture, notifies saidpicture coding means of the reception, and said picture coding means,upon receiving the notice from said picture receiving means, changes thecoding format to the in-frame coding format.
 23. A multicast meetingprogram for carrying out multicast meeting by a computer to execute thesteps of: inputting a picture stream to a picture input means such as acamera of a multicast meeting unit; coding the input picture stream by apicture coding means of the multicast meeting unit to prepare the codedpicture information to be transmitted; transmitting the coded pictureinformation by a picture transmission means to a network by use of themulticast; making a picture receiving means receive the pictureinformation transmitted by use of the multicast; decoding the receiveddata by a picture decoding means of the multicast meeting unit;displaying the decoded picture stream on a picture display means of themulticast meeting unit; and storing, in a coding information storingmeans, the coding parameter of terminals that are participating in ameeting and terminals that participate in the meeting in the middle, ifa terminal participates in the meeting in the middle, wherein saidpicture coding means codes the picture data by use of a changed codingparameter that can be displayed on all the terminals that areparticipating in the meeting with reference to said coding informationstoring means.